Unlevel ladders have been a problem to mankind literally for many centuries. It is well known that when a ladder is not level and a person climbs said unlevel ladder, the ladder can (and is likely to) slip to one side or the other and the person can be severely injured. Accordingly, over the years, people using ladders have made efforts to level the ladders upon which they were climbing. Most of the efforts have been directed to providing adjustable sections of metal or wood which are arranged as, or attached to, the lower extremities of a ladder. Such adjustable sections usually permit the ladder to be raised or lowered on both sides and, in use, of course, normally one side is adjusted to raise or lower that one side of the ladder, thereby leveling the rungs with the ground, or leveling them with whatever the base might be upon which the ladder is resting.
Such mechanical devices have been cumbersome and expensive, although indeed philosophically they have been effective. A ladder purchased in the present day, at a hardware store, or lumber company, normally does not include a leveler mechanism as part of the package because of the expense and/or cumbersome aspects of these devices.